And wasn't it very muddy on the outside? Much dirtier than if it just did short drives in town?
Driving up to Center Road isn't exactly "in town." If you'll remember from from Offroadrunner's video, that road is out in the boonies, and there was a lot more snow up on that hill (in the video) than down in lower elevations. Also, if GR approached from the same direction that orr did, he'd have had to turn around before leaving the body (probably) to get on the side of the road with the drop off. While turning around -- in a driveway or whatnot -- he may have gotten a bit stuck in some mud (from rain/snow earlier that week) and splattered mud up on his vehicle. Or, the same thing could have happened when he pulled over to dispose of the phone. Or he could have originally decided to go down one of the little side roads off Center Road (the trail head for a well-known running trail is there -- he may have headed to the trail head, and maybe some people were there, so he had to change plans -- that area is grassy/muddy -- not paved all the way in).
I agree that the phone could have been disposed of later -- he might have forgotten it earlier. However, it does seem significant that the place where the phone was left was on the way from their home to where Jen's body was left, and also on the way from where her body was found to the apartments. So, I tend to believe that it was all done at one time.
There would have been plenty of time, even in the 74 minutes from the last time Jen's phone pinged in the house to when GR showed up at the Y. In the video, it only took 19 minutes to go from where the phone was left to where the body was left and then to the Y. I think I remember it was only about a mile from the apartments to the Y, so that would be an easy 10 minute downhill jog. So that's just 30 minutes there, leaving 44 minutes to get from the house to the sand hill (area where phone was left). I couldn't find Offroadrunners's other video from the house to the sand hill, but it certainly didn't take that long.
ETA: I just googled it, and it's only about a 20 minute drive from their house to where the phone was found. And, we know from Offroadrunner's video, that from that point to where the body was left, and back to where the phone was left, and then to the apartments is 19 minutes (including about a one minute stop where the body was left). Then, a 10 min. jog from the apartments after leaving the van to the Y -- the whole process from leaving the house to arriving at the Y could have easily been done in under an hour -- leaving plenty of time to scope out potential spots to leave the body along the way or whatever.